Among the issues, warn the former heads of the panel, is the unreliability of the system to keep airline passengers from smuggling explosives onto a plane.

Reporting from Washington — Despite the outlay of hundreds of billions of dollars and a vast reorganization of federal agencies since the Sept. 11 attacks, major gaps remain in the government's ability to prevent and respond to a terrorist strike, according to an assessment by the former heads of the 9/11 Commission.

The report, which will be released Wednesday, warns that the nation's ability to detect explosives hidden on passengers boarding airplanes "lacks reliability." It describes emergency communications used by first responders in urban areas as "inadequate." And it calls efforts to coordinate rescues "a long way from being fully implemented."

The panel, formally known as the National Commission on Terrorist Attacks Upon the United States, was created by Congress in late 2002 as an independent, bipartisan group to investigate the hijackings of four jetliners by Al Qaeda operatives. Its final report included numerous recommendations for reforms in the intelligence, law enforcement and domestic security communities.

The new assessment comes from the panel's former chairs, former Republican New Jersey Gov. Thomas H. Kean and former Rep. Lee H. Hamilton (D-Ind.).

The committee also faults the Department of Homeland Security and Congress for failing to create a way to track when people leave the country and for not implementing tougher security requirements for identity cards.

"A decade after 9/11, the nation is not yet prepared for a truly catastrophic disaster," says the report, titled "Tenth Anniversary Report Card: The Status of 9/11 Commission Recommendations."

"Until some of these things are done, we aren't going to be as safe as we should be," Kean said in an interview.

Kean said it was "outrageous" that Congress had not passed a law to allocate new radio spectrum to first responders.

The inability of firefighters and police to talk to each other from the rubble of the World Trade Center and the Pentagon was a "critical failure" on Sept. 11, 2001, according to the report, but a recommendation to dedicate radio spectrum for first responders has languished in Congress.

In February, President Obama called for $7 billion to build an emergency broadband network using a designated band of radio spectrum known as D-block. But such a bill has not come to a vote in the Senate, and the House has not considered it.

More than a year and a half after Umar Farouk Abdulmutallab, the so-called underwear bomber, passed through airport screening in Amsterdam and boarded a Christmas Day flight with plastic explosives sewn into his undergarments, the U.S. screening system "still falls short in significant ways," the report says.

The new full body scanners "are not effective at detecting explosives hidden within the body and raise privacy and health concerns," it says.

Some of the hijackers on Sept. 11 used fake documents to obtain state-issued IDs to board the airplanes, but deadlines issued in 2008 for states to make driver's licenses more difficult to forge have been pushed back multiple times. Compliance is currently not required until January 2013.

The delay "makes us less safe," the report says.

Another recommendation that has been ignored: for the U.S. government to fingerprint visa holders as they leave the country.

A system that tracks when travelers exit the U.S. would be "very expensive" to implement, said Stewart Baker, former head of policy at the Department of Homeland Security.

"This is a rare circumstance where I think the 9/11 Commission is wrong," Baker said. "I don't see the counter-terrorism value."

Rick Nelson, a counter-terrorism expert at the Center for Strategic and International Studies, a Washington think tank, said some of the recommendations went unfollowed because they would either be too expensive or they ran afoul of concerns about privacy and civil liberties.

"A lot of the work that remains requires a decision by Congress and ultimately the American people," Nelson said. "Do they want this increased security and are they willing to pay for it and give up some civil liberties?"